In an aluminum electrolytic capacitor, when an excess voltage or reverse voltage is applied or when an excess current flows due to longevity or failures, etc., an organic solvent composing a driving electrolyte impregnated in a capacitor element evaporates or the electrolyte is pyrolyzed (thermally decomposed) to generate a vapor due to a temperature rise, or the electrolyte is decomposed by an electrochemical reaction to generate a hydrogen gas or vapor, consequently, an internal pressure rises inside a metal case made by aluminum.
At this point, when there is no way out for the gases, an explosion is caused as a result that the internal pressure of the metal case surpasses a sealing force of the metal case. Therefore, in a conventional aluminum electrolytic capacitor, an explosion-proof valve formed by a thin portion is normally provided on a top panel of its metal case.
As explained above, when the internal pressures of the metal case rises abnormally, the explosion-proof valve opens and a gas of an organic solvent and a hydrogen gas composing the driving electrolyte in the metal case explained above flow out, so that it safely results in a failure without an explosion of the electrolytic capacitor.
According to the configuration above, however, there is a disadvantage that the driving electrolyte flows to the outside and adheres to the substrate, on which the electrolytic capacitor is set, and other electronic devices, and short-circuiting, tracking and other electric abnormalities are caused. Also, a vapor and a foreign odor of the driving electrolyte belching from the explosion-proof valve may possibly give the user a false idea that it is due to some ignition.
As a countermeasure of the above disadvantage, an electrolytic capacitor attached with an extensible cap has been proposed (refer to the patent document 1). Also, an aluminum electrolytic capacitor having an absorbent, which has a property of absorbing a driving electrolyte and breathabilily, finished with a flame-retardant treatment, provided above an explosion-proof valve of the electrolytic capacitor has been proposed (refer to the patent document 2). Furthermore, an aluminum electrolytic capacitor having a granular gelator having a behavior of turning the driving electrolyte into gel provided above an explosion-proof valve has been proposed (refer to the patent document 3).